1. Field of the Invention
The present invention broadly relates to brackets and ligatures used in orthodontic treatment. More specifically, the present invention relates to an assembly of an orthodontic bracket and a latch for releasably retaining an archwire in an archwire slot of the bracket.
2. Description of the Related Art
Orthodontic therapy is a specialized type of treatment within the field of dentistry, and involves movement of malpositioned teeth to orthodontically correct locations. Orthodontic treatment often improves the patient's occlusion and typically enhances the aesthetic appearance of the teeth.
Many types of orthodontic treatment programs involve the use of a set of tiny appliances and wires that are commonly known collectively as "braces". During such treatment programs, small appliances known as brackets are fixed to the patient's anterior, cuspid and bicuspid teeth, and an archwire is inserted into a slot of each bracket. The archwire forms a track to guide movement of the teeth to orthodontically correct locations. End sections of the archwires are typically captured in tiny appliances known as buccal tubes that are fixed to the patient's molar teeth.
Orthodontists often use ligatures to connect the archwire to the brackets and to urge the archwire into an orientation of seating engagement in the archwire slot. One type of commercially available orthodontic ligature is a small, elastomeric O-ring. Orthodontic O-rings are installed by stretching the O-ring around small wings (known as "tiewings") that are connected to the bracket body on the gingival side (i.e., the side closest to the patient's gingiva or gums) and on the occlusal side (i.e., the side closest to the outer tips of the teeth) of the archwire slot. Once installed, the O-ring ligature extends around the tiewings as well as over the labial side of the archwire (i.e., the side closest to the patient's lips or cheeks) and urges the archwire toward a lingual wall (i.e., the wall closest to the patient's tongue) of the archwire slot.
Metal ligatures, such as ligatures made of stainless steel, are also used to retain archwires in archwire slots of brackets. Metal ligatures are typically made of a short section of initially straight wire. During installation, the wire ligature is hooked around the tiewings and extended over the labial side of the archwire, and end sections of the ligature are then twisted together to form a loop to retain the ligature in place.
Unfortunately, some orthodontists are not entirely satisfied with conventional elastomeric and metal ligatures. Such ligatures are somewhat time-consuming to install, both during initial installation and also during reinstallation whenever replacement of the archwire or ligatures is desired. As can be appreciated, a savings in the amount of time needed for ligation can help to reduce the total time that the practitioner must spend with the patient and consequently aid in reducing the overall costs of orthodontic treatment.
Other disadvantages are also associated with elastomeric and metal ligatures. For example, there have been reports that certain polyurethane elastomeric ligatures have exhibited deformation and force decay during the course of treatment. In some instances, elastomeric ligatures are stained by food and beverages consumed by the patient and become somewhat unsightly. Metal ligatures often have sharp ends that may retain plaque and food debris and also may increase the risk of infection.
In an effort to overcome the problems associated with conventional ligatures, a variety of orthodontic brackets have been proposed having various types of latches for coupling the archwire to the bracket. Such brackets are also known as self-ligating brackets. The latch comprises a clip, spring member, cover, shutter, bail or other structure that is connected to the bracket body for retaining an archwire in the archwire slot.
Examples of self-ligating orthodontic brackets having generally U-shaped ligating latch clips are described in U.S. Pat. Nos. 3,772,787, 4,248,588 and 4,492,573. In general, the clip of such brackets is slidably mounted on the bracket body, and a dental explorer or other small-tipped dental tool is used to move the clip relative to the body when needed in order to open or close the archwire slot. A self-ligating bracket known as the "Speed" brand bracket also has a movable, generally U-shaped clip for ligating the archwire to the bracket.
Other types of self-ligating brackets have latches that resemble swinging shutters or closures that pivotally move between a slot-open and a slot-closed position. For example, U.S. Pat. No. 4,712,999 has a rotatable cover plate that is pivotally connected at one end to a tiewing of the bracket along one side of the slot, and is releasably engagable at the other end with a tiewing that is located along the opposite side of the archwire slot. Other orthodontic brackets with swinging latches are described in U.S. Pat. Nos. 4,103,423, 5,516,284 and 5,685,711.
U.S. Pat. Nos. 4,371,337 and 4,559,012 describe self-ligating orthodontic brackets having latches that rotate about the longitudinal axis of the archwire slot. The latch of these references has a somewhat cylindrical shape and is rotatably received in a mating, cylindrical channel, and an outwardly extending arm is provided to assist in rotatably moving the latch between a slot-open and a slot-closed position.
A self-ligating orthodontic bracket that is described in U.S. Pat. No. 5,711,666 has a ligating latch that comprises a flexible flat spring member. One end of the spring member is fixed to the bracket body on one side of the archwire slot, and the opposite end of the spring member has notches that releasably engage latch sears or catches when the spring member is moved to a slot-closed position. To open the slot, the notches are disengaged from the catches and the spring member is bent to an orientation sufficient to enable the archwire to be removed from the archwire slot.
Other types of self-ligating orthodontic brackets have latches that comprise essentially flat plates that are slidable between a slot-open and a slot-closed position. Examples of such construction are shown in U.S. Pat. Nos. 5,094,614, 5,322,435 and 5,613,850. In general, the sliding latches described in those references move in upright channels that are located buccolabially of the archwire slot.
Another type of self-ligating bracket that has been proposed in the past has a latch that is made of a section of wire material that functions similar to a bail. The orthodontic brackets described in U.S. Pat. Nos. 4,149,314, 4,725,229 and 5,269,681 have wire-like latches that swing between a slot-closed position and a slot-open position. The orthodontic brackets described in U.S. Pat. Nos. 4,197,642 and 4,260,375 have a wire latch that is slidable between a slot-open and a slot-closed position.
Many practitioners prefer self-ligating orthodontic brackets over brackets that are not self-ligating because handling of an initially separate elastomeric O-ring or a metal ligature wire can be avoided. However, certain types of conventional self-ligating orthodontic brackets are not entirely satisfactory because the costs of manufacture are relatively high. The relatively high manufacturing costs are due, in part, to the fact that many of the components of conventional self-ligating brackets are of a specialized nature and have no other use or function. As a result, lower costs or discounts that are often associated with larger volumes of production are not obtained.
Another problem often associated with conventional self-ligating brackets relates to the general lack of treatment options often afforded by such brackets. For example, the orthodontist may change treatment techniques during the course of treatment and determine that a hook should be connected to a certain bracket. Alternatively, the orthodontist may determine that a particular bracket should provide increased rotational force on the associated tooth in order to better move the tooth to its intended location. Unfortunately, hooks and ligatures providing rotational forces cannot be connected to many conventional self-ligating brackets and, under those circumstances, the orthodontist may debond the self-ligating bracket originally installed and replace it with another bracket that provides such features. As can be appreciated, such removal and replacement of a bracket during the course of treatment represents a time-consuming and costly nuisance for both the practitioner as well as for the patient.
There is a clear need in the art for an orthodontic bracket that provides the features and functions of conventional self-ligating brackets and yet provides, when desired, the features and functions of conventional brackets that are not self-ligating. In this manner, the practitioner can carry out a variety of treatment options using well known and familiar techniques. Moreover, it would be a clear advantage if such a bracket were relatively inexpensive to manufacture in comparison to conventional self-ligating brackets.